It was the old "it's not you, it's me" routine that Pep Guardiola pulled on Samuel Eto'o back in July when he jilted the Cameroon striker just weeks after celebrating the greatest season in Barcelona's history with him.

Eto'o had scored the decisive goal that helped win Barcelona the Champions League, and 33 others that helped them win the treble but was being bundled off to Internazionale along with €40m (£36m) in exchange for Zlatan Ibrahimovic.

Guardiola explained he just didn't have any "feeling" with the forward and felt it was time for a change. Tonight Eto'o faces his old boss and his replacement, Ibrahimovic, in an opening group match that should have knockout-stage intensity.

It is an encounter that also sees Jose Mourinho face his former club and the one that overlooked him for the job of coach last season. But for once Mourinho is not the main event – that will be the duel between Eto'o, scorer of 108 goals from 145 league appearances in five seasons for Barcelona, and Ibrahimovic, a player valued – at least by Barcelona – as €40m better than his predecessor.

Eto'o has already lit the fuse. "I would like to know exactly what Guardiola meant by 'feeling'?" he said in the run-up to tonight's game. He is free to choose who he works with but things could have been sorted out in another way."

Guardiola has taken full responsibility for the decision to replace Eto'o with Ibrahimovic. The players' styles are markedly different but the Barça coach has always been an admirer of the languid former Ajax prodigy and believes he can change both the way the player – and if he has to, even the team – play, to make things work. The 27-year-old Swede is renowned for not delivering in big matches. Former Milan coach Arrigo Sacchi once commented: "He is strong against the weak but weak against the strong."

Eto'o is the antithesis of a big-game bottler. Barcelona won more European Cup finals with him than they had won without him. Twice he scored in finals and they were not decoration goals in games already decided but vital strikes – the equaliser against Arsenal in 2006 and the effort that broke the deadlock against Manchester United last season.

"A lot of the time he doesn't even know what he is going to do or where and when he is going to shoot. He is a very intuitive player," says Barcelona's goalkeeping coach Juan Carlos Unzue. Barça defender Gerard Pique adds: "He is always putting pressure on the opposition. He is extremely mobile, constantly willing to run the channels – he simply does not stop."

Pique's comments are echoed by keeper Victor Valdes who describes Eto'o as "unpredictable, lightning fast and lethal in front of goal" and by Barcelona captain Xavi who says: "I have a weakness for Samuel. He is quite simply one of the best strikers ever to pass through this club."

Eto'o believes that support from his former team-mates makes a nonsense of the suggestion that he was moved on because he was a bad for dressing-room harmony. He says: "When I joined the club they were my team-mates. When I left they were my friends. I still speak with most of them. I was never a problem. All such talk is from the first word until the last word lies." Eto'o is also unhappy at suggestions he never wanted to sign a new deal at the club.

Barcelona say they made him an offer and he was then unreachable when they tried to contact him for a response. In truth the offer was one the club knew the player would refuse and it was sent as a text message to his agent, hardly wrapped with ribbons and bows. Eto'o adds: "They say they could not reach me but they have always managed to do so in the past."

If Eto'o's departure was bitter, Ibrahimovic's was at first amicable. He wanted to leave and Mourinho, who first tried to sign Eto'o when he was Chelsea manager, was happy for the deal to take place – especially in view of the fact he would get some of the extra €40m Inter received, enabling him to go out and buy Wesley Sneijder from Real Madrid just before the deadline.

Some animosity has since surfaced, however, among Inter fans, after Ibrahimovic was pictured kissing his badge on his first day at the Nou Camp. And it increased after recent comments that he felt the club's last three Scudettos had been mainly down to him.

"Inter has been in existence for more than 100 years – they'd already won a few things before he turned up," said Inter winger Mancini in response. Ibrahimovic had been quoted as saying: "The club had gone many years without winning anything and then for three years running we won the League. I made the team win again after 17 years."

In the build-up to tonight's game he has been asked about his performances in big matches. He said: "I am happy with myself. You only have to look at the titles I have won."

Swedish journalists say privately the player is more than aware of his reputation and it bothers him that especially in England he has no real kudos. A Champions League medal with a few big European performances along the way would end that debate. And what better place to start than in his old stadium.

For Eto'o, Champions League success in May's final in the Santiago Bernabeu, Real Madrid's stadium, would complete an extraordinary hat-trick of European Cups. He once had to apologise for leading 100,000 celebrating Barcelona fans in chants of "Madrid bastards, salute the champions" after Barça had just won the League. Back then the anger that serves as a fuel-injection to his football was all directed at the capital club who sold him to Barcelona. Winning the final in Madrid would be getting back at both clubs.

Mourinho did his best to spice things up further this week by saying Eto'o was the best striker he had ever coached – something he had said about Ibrahimovic last season. The Inter manager has his own reasons for wanting to put one over on tonight's Catalan opponents. In January 2008, he met with Barcelona vice-president Marc Ingla and sporting director Txiki Begiristain in Lisbon to discuss the possibility of him becoming Barça's new coach at the end of that season. The club had already decided to fire Frank Rijkaard at the end of the campaign but ultimately Mourinho was considered too outspoken and controversial and was overlooked.

Maybe that's what he sees in Eto'o – a risk Barcelona felt they could no longer afford to keep on taking after his outburst in the middle of the 2006-07 season directed at Rijkaard and an underperforming and almost-never-training Ronaldinho, and a similar tirade the following season in which he admitted he would leave if the club won nothing.

Giving him a new deal would have been a gamble according to those who backed his departure. His supporters suggest that to sell the man who won Barcelona two Champions Leagues and replace him with someone who at his last club hit the net just six times in 22 matches in Europe represents a far bigger risk.